Recently, interest in energy storing technologies is gradually increasing. As application areas expand to energies for mobile phones, camcorders and notebook PCs, and further, electric vehicles, efforts for research and development on electrochemical device are gradually materializing. Electrochemical device is a field gathering the most attention in this aspect, and especially, development on chargeable and dischargeable secondary batteries is becoming the focus of interest.
Of the secondary batteries that are currently being applied, the lithium secondary battery developed in the early 1990s is coming into the spotlight due to advantages of higher operating voltage and greater energy density compared to conventional batteries such as Ni-MH.
Generally, a lithium secondary battery is manufactured by storing an electrode assembly consisting of a cathode, an anode and a separator interposed there between, in a battery case, and then injecting electrolyte. Here, if the adhesion strength of the electrode and the separator included in the lithium secondary battery is weak, it affects the performance and safety of the battery. Therefore, in order to secure the adhesion strength of the electrode and the separator, an adhesion layer is formed on a surface of the separator, and in prior art, as the adhesion layer, a binder layer used to be formed by inducing phase separation on the surface of the separator, in which case thinning the binder layer was difficult. For realizing the performance of the battery, especially, for excellent output, the binder layer needs to be formed as a thin film, and maintain a porous structure.